Hydraulic variable volume clearance pocket device



July 24, 1962 K. H. WHITE 3,945,892

HYDRAULIC VARIABLE VOLUME CLEARANCE POCKET DEVICE Filed Sept. 25, 1959 INVENTOR KEg/VETHHWH/TE HIS ATTORNEY United States atent fiiice 3,045,892 Patented July 24, 1962 Filed Sept. 23, 1959, Ser. No. 841,841 4 Claims. (Cl. 230-41) This invention relates to pump control systems, and more particularly to the clearance pocket piston and motor for use in a variable clearance capacity control system for reciprocating piston type gas pumps.

In pumps of this type, as for example, reciprocating air compressors, a method of controlling the capacity of the compressor is to provide a single variable volume clearance pocket having a maximum volume sufiicient to completely unload the compressor (see US. application Serial No. 578,639, filed April 17, 1956). The volume of the clearance pocket is varied in accordance with the demand on the compressor and the capacity of the compressor can be varied throughout the entire range from full capacity to no capacity. With this exceedingly fine capacity control the capacity of the compressor is made to match the demand on the compressor. Therefore, the capacity control system is one in which the capacity of the compressor can be varied in infinitely small steps throughout the entire capacity range of the compressor by use of a fluid motor having a follow-up system or servomotor.

The primary shortcoming in mechanisms of this type is that in case of failure of the motor or feed back system the machine must be shut down for repairs, blowing down of the pressure in the compressor. This means disrupts the entire machine for a major disassembly, and before restarting, it would be necessary to purge the system of the air which in some cases could contaminate the process.

It is an object of this invention to provide a variable volume clearance pocket for reciprocating piston type gas pumps adapted to be prepositioned and maintained to permit operation of the machine when the automatic controls for such clearance pocket are removed for repairs without disturbing the machine.

This and other objects will become apparent by reference to the following description and accompanying drawings in which FIGURE 1 is an elevational view, partly in section, of a clearance pocket casing and piston together with the operating motor in accordance with the invention,

FIG. 2 is an elevational view similar to FIGURE 1 incorporating the maintaining structure replacing the motor in accordance with the invention, and

FIG. 3 is an enlarged sectional view of the connection between the piston and the motor.

Referring now to the drawings and specifically FIG. 1, the cylinder of the compressor has a head 12 which may be bolted thereto through a flange 14. The head 12 has a center bore 16 which forms the variable clearance pocket with a smaller bore 18 through the end wall thereof which connects the pocket 16 to the cylinder chamber in the cylinder 10. A piston 20 is slidably received in the clearance pocket 16 and has the usual peripheral rings 22. The end of the pocket 16 is closed by a unitary cover 24 and motor adapter 28, the cover 24 being bolted to the head casing 12. The cover 24 has a central opening 26 suitably packed to provide a passage for a piston rod 34 connected at one end to the piston 20. The cover 24 and the motor adapter 28 are spaced from one another by integral legs which form a pocket 32. An axial motor 36, in the form of a cylinder 38 and a piston 40, is mounted on the adapter 28. The piston 40 has a piston rod 42 extending through an opening 30 in the motor adapter 28 that connects to the piston rod 34. The piston 40 is actuated by controlling the supply and exhaust of liquid under pressure to the motor chambers 41 and 4.3 to move the clearance pocket piston to the desired position. The afore mentioned patent application discloses a control for the supply of such liquid.

Referring more specifically to FIG. 3, the piston rod 34 has an axial peripheral slot 46 and a reduced threaded end 48. The threaded tip member 48 extends through an opening 54 in a servo or follow-up control arm 44 and threadedly engages a tapped hole 50 in the piston rod 42 of the motor 36. To prevent relative rotation between the piston rod 34, the piston rod 42 and the servo arm 44, a threaded fastener 58 extends through a small opening 56 in the follower arm 44 and engages a tapped hole 52 in the piston rod 42. The head of the fastener 58 extends outwardly of the arm 44 in the slot 46. The motor 36 receiving fluid at either motor chamber 41 or 43 moves the piston 20 in the clearance pocket 16 to vary the size of the pocket communicating with the inside chamber of the cylinder 10 determinate upon the demand of the compressor.

Should the motor 36 or the associated control system (not shown) break down the control for the variable clearance pocket may be altered in the following manner in accordance with the invention as shown in FIG. 2. The fastener 58 is withdrawn from the threaded opening 52 and the opening 56 in the arm 44. The motor 36 is removed from the motor adapter 28 and the piston rod 42 is unscrewed from. the piston rod 34. A threaded rod member 60 having a tapped hole (not shown), similar to hole 50, is screwed on to the threaded fastener portion 48 of the piston rod 34 and extends through the opening 30 in the motor adapter. A nut holder 62 is now bolted on to the motor adapter 28 and carries a nut 64 which engages the external threads on the member 60 and has a hand wheel 66 attached thereto for rotation. A. jam nut 68 is threaded on to the member 60 and has a handwheel 70 for the rotation thereof. The arm 44 of the follow-up mechanism (not shown) is still retained on the threaded end portion 48 of the piston rod 34 and is clamped thereto by the threaded member 60. The piston 20 may now be positioned in the pocket 16 by rotation of the handwheel 66 which rotates the nut 64 carried by the nut holder 62 feeding the threaded member 60 towards or away from the pocket determinate upon the direction of rotation of the nut 64. When the piston 20 has been positioned, the handwheel 70 is rotated moving the nut 68 toward the nut 64 on the threaded member 60 to lock the handwheel in position. Thus it can be seen, that the compressor has not been open to atmosphere in removing the power portion of the variable clearance pocket arrangement and thus does not have to be blown down nor purged. The piston 20 being held in a fixed position without its power control, permits the compressor to be used while the power control is being repaired.

Having thus described my invention, I claim:

1. An adjusting and holding means for a motor operated variable clearance capacity device when its motor is removed and having a cylinder providing a pocket, a moveable piston in the pocket to adjust the pocket capacity and having a piston rod member extending out of the pocket with means for connecting to the motor, and an adapter connected to the cylinder for mounting the motor; comprising a threaded member connected to the piston rod member motor connecting means, a nut holder mounted on the motor adapter, and a nut rotatably mounted in the nut holder and threadedly engaging the threaded member for moving the piston when such nut is rotated, said nut having means engaging both ends of the nut holder to prevent axial movement of the nut.

2. The adjusting and holding means according to claim 1 wherein a lock nut threadedly engages the threaded member for moving axially thereon when rotated to abut the nut and lock the threaded member to hold the piston in a predetermined position, and each of the nuts having means to be engaged for manual rotation.

3. An adjusting and holding means according to claim 1 wherein a follow-up arm for a servo control that is held between the piston rod member and the motor is locked between the piston rod and threaded members.

4. An adjusting and holding means according to claim 3 wherein one member has an axial slot in it and a threaded tip portion extending from its end, the arm having a first bore for passing over the threaded tip portion and a second bore alined with the slot, the other member having a first threaded bore for receiving the threaded tip portion to join the two members together with the arm being retained therebetween and a second threaded bore, and a threaded fastener passing through the second bore in the arm, threadedly engaging the second threaded bore and having a portion disposed in the slot to prevent relative rotation between the two members.

References Cited in the file of this patent UNITED STATES PATENTS 1,867,681 Simson July 19, 1932 1,969,507 Gehres Aug. 7, 1934 1,985,642 Moody Dec. 25, 1934 2,047,167 Heller July 7, 1936 FOREIGN PATENTS 257,956 Switzerland Oct. 31, 1948 

